A problem long-standing in the automotive field lies in production of pneumatic tire and wheel assemblies that, when assembled and operated on a vehicle, run true about their axis of rotation. Forces generated by any circumferential variations in the tire carcass and/or out-of-round condition in the tire or wheel causes vibrations, which in turn lead to dissatisfied customers and significant warranty claims against automobile manufacturers. The present trend among manufacturers toward higher tire inflation pressures, smaller vehicles and tighter vehicle suspensions to improve fuel economy accentuates this problem, so that uniformity of radial run-out and force variations of the tire and wheel assembly has become more critical than in the past.
Vehicle wheels conventionally include a circular array of disc bolt openings adapted to receive studs for fastening the wheel to a vehicle, and a center-pilot opening adapted to be received over the wheel hub. It has been and remains conventional practice in the industry to attempt to form the bolt circle and center-pilot openings coaxially with each other and with the rim bead seats, with the goal thus being a perfect true-running wheel. A number of techniques have been proposed for accomplishing this result, including formation of the bolt and center openings with a single tool while locating off of the bead seats, machining the center opening while locating off of preformed bolt openings, and/or circumferentially permanently deforming the rim bead seats while locating off of the bolt and/or center-pilot opening.
Daudi et al U.S. Pat. Nos. 4,279,287, 4,354,407 and 4,573,338 all assigned to the assignee hereof and incorporated by reference herein, depart from the conventional practice of attempting to form a true-running wheel, and address the problem of radial run-out and/or radial force variation in a pneumatic tire and wheel assembly by intentionally forming the bolt openings and/or center-pilot opening in the wheel disc at the time of wheel manufacture on an axis that is eccentric to the average axis of the rim bead seats. (It is understood in the art that the average axis of the bead seats is the average axis of one bead seat averaged with the average axis of the other bead seat, for example by measuring the bead seats simultaneously.) This eccentricity is in a direction and amount that is predetermined to locate the low point or high point of the first harmonic of bead seat radial run-out circumferentially adjacent to a selected location on the wheel rim. In the preferred embodiments, the low point of the first harmonic of bead seat radial run-out lies substantially within a quadrant centered on the valve stem opening in the rim. A pre-tested tire having the location of the high point of the first harmonic of radial force variation marked thereon may then be assembled to the wheel with tire mark aligned with wheel valve stem opening so that the respective tire and wheel harmonics are complimentary and thereby tend to cancel each other.
In the preferred wheel forming apparatus disclosed in the above-noted Daudi et al U.S. Patents, the bolt and center-pilot openings are formed by separate punches fixedly mounted on a single punch assembly that substantially simultaneously punch-forms all the mounting openings in a wheel disc while the wheel is located by fixturing the same about the rim bead seats. Daudi U.S. Pat. Nos. 4,736,611 and 4,819,472, also incorporated by reference herein, disclose a modified method and apparatus for forming the bolt and center-pilot openings in which a preformed wheel is engaged and fixtured around the rim bead seats with the inboard disc face resting on a lower die assembly and without plastic deformation to the rim or disc. An upper die assembly having an array of bolt hole punches is moved into piercing and coining engagement with the disc to form the bolt openings. Continued motion of the upper die assembly pushes the disc and lower die assembly into shearing engagement with a center punch that forms the center-pilot opening. The axis of the bolt openings and/or center-pilot opening and/or bead seats may be concentric with or eccentric to each other.
A problem with the apparatus disclosed in the above-noted patents lies in the fact that the several locators that engage the rim bead seats, which collectively define the location of the average bead seat axis of the wheel relative to the tooling set-up during the forming operation, require individual adjustment by relatively skilled technicians. Whether forming the mounting openings (i.e., the bolt openings and/or the center-pilot opening) concentric with or eccentric to the rim bead seats, it is desirable that the array of bead-seat-engaging surfaces of the locating jaws be substantially concentric with each other when engaging the rim bead seats during the forming operation. Added to this, of course, is the complexity of adjusting the individual locating jaws so that their average axis is either precisely concentric with the hole-forming mechanism, or eccentric thereto by a precise and desired amount. The current practice is to adjust the several jaws with respect to a centrally located gauge to positions believed to locate the average bead seat axis at the desired position, run a representative sample such as five wheels through the apparatus, and measure position of the average bead seat axis relative to the bolt and/or center-pilot mounting openings. If the measured bead seat axis is not at the desired location with desired statistical consistency, individual locating jaws are adjusted in an attempt to improve position and/or statistical consistency of the bead seat axis location. The jaws to be adjusted and the amount of adjustment to each jaw are empirically determined by the technician based upon training and experience. The entire process is repeated until the average axis of the bead seats in wheels produced by the apparatus is at the desired location with the desired statistical consistency.
It is a general object of the present invention to provide improved apparatus for forming mounting openings in vehicle wheels having facility for easy, more precise and economical adjustment of concentricity/eccentricity of the mounting openings with respect to the rim bead seats.